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The Perth Group :
These papers contain the recommendations that in order to prove material banding at 1.16 g/ml is retroviral, it should be subjected to the following assays:
(a) physical‑‑EM for virus count, morphology and purity;
(b) biochemical‑‑RT activity, viral and cellular RNA, total protein, gel analyses of viral and host proteins and nucleic acids;
(c) biological‑‑infectivity in vivo and in vitro.
And there should be “No apparent differences in physical appearances” between the particles seen.